AFAIK, right now, there’s nothing available for something like Corne-ish Zen that would be as quiet as a standard chiclet-style keyboard (like your Macally). The Corne-ish Zen takes Kailh Choc v1 switches, and a linear switch (like Kailh Choc Red, Pro Red, or Silver, for example) are going to be the quietest kind. I’m typing on a keyboard right now with Kailh Choc Red switches, and it’s quiet for a mechanical keyboard, but a little louder than typing on a standard laptop keyboard, for example.

There are some switch mods out there that aim to make Choc v1 switches quieter, like “tape mod” or “floss mod”, although mods like this tend to be pretty tedious and time-consuming. There will probably be a “silent” Choc v1 switch someday, but I don’t even know offhand if one is in the works.

If you were interested in a non-low-profile mechanical keyboard, there are “silent” switches available for those (a few examples are Cherry MX Silent Red, ZealPC Zilents, and Kailh Box Silent Brown). If you type with a light touch, a silent mechanical switch might be almost as quiet as your Macally keyboard.

tl;dr: A Corne-ish Zen will be fairly quiet with a linear switch, but not as quiet as the Macally keyboard.